This invention relates to self-standing blown plastic containers. It has particular relation to pressure resistant bottles such as used for carbonated beverages, or the like, formed of bi-axially molecularly oriented polyethylene terephthalate. However, the principles of the invention may be applied to non-pressure containers, such as for wine, water, or the like, and the principles further are not intended to be limited to bottles formed of polyethylene terephthalate (PET), although the use of such material is preferred.
Blown pressure vessels in the form of plastic bottles formed of PET material have come into general use as disposable containers for carbonated beverages. In order to obtain the desired bi-axial orientation and to provide the preferred shape as a pressure vessel, such bottles have commonly been made with rounded or semi-spherical bottoms. In order to support such bottles in an upright position for filing, shelving and the like, auxiliary base cups, usually formed of polyethylene or polypropylene, assembled on the bottle after blowing, have come into widespread usage, as shown for example in Chang U.S. Pat. Nos. 4,436,216 issued Mar. 13, 1984 and 4,438,856 issued Mar. 27, 1984.
The industry has recognized the desirability of eliminating such base cups due, to the additional expense and inconvenience involved. The additional expense includes not only the cost of the cups themselves, but the cost and maintenance of the attendant separate lines of equipment to produce and handle the cups, and to assemble and glue or weld the same over the bottoms of the bottles. The recycling of such bottles also presents special problems due to the necessity for removing the base cups to separate the material of the base cups from the material of the bottles themselves. Various attempts have been made to produce bottles formed of bi-axially oriented plastic material, such as PET, which are free standing on the bottom, using only plastic material which is integral with the bottle itself. Thus, carbonated beverage bottles have been proposed with "champaign" bottoms such as in Aoki U.S. Pat. No. 4,465,199 issued Aug. 14, 1984 and Gittner et al U.S. Pat. No. 4,177,239 issued Dec. 4, 1979, in which the bottom end wall is formed with an inwardly convex surface. The pressure within the bottle tends to cause the bottom to reverse or bulge out, and this must be resisted by adding material to the inwardly directed convex curve or fold forming the champaign bottom. Further, it is difficult, if not impossible, to achieve the desired bi-axial orientation in the bottom material itself, for optimum strength and stress crack resistance.
Carbonated beverage bottles are also being made with a bottom in which pentaloid leg portions are formed in the bottom wall, which partially project outwardly, to form support or locating feet, as shown in U.S. Pat. No. 3,598,270 and U.S. Pat. No. 4,518,558 issued May 21, 1985 to Anway et al. While carbonated beverage bottles having such pentaloid legs have been successful, they are subject to stress cracking, and further do not provide an annularly uniform support as to permit the bottle always to stand upright on a wire shelf.
Annularly continuous integral base supports have been suggested in Uhlig U.S. Pat. Nos. 3,843,005 and 3,949,034. These supports are in the form of double-walled depending skirts which are pinched off, in the blow-molding process, from the material making up the bottom wall of the parison or preform, and are pressure molded into a skirt of ring shape during the blowing step. While such concept provides a useful and continuous support from a mechanical point of view, it severely reduces the pressure strength of the container as a pressure vessel and impairs the integrity of the vessel. This is particularly true when PET material is used, since it does not weld readily to itself, and a low or weak molecular bond is formed between the adjacent layers making up the skirt. Accordingly, the strength of the bottom is dependent primarily upon the mechanical strength of the fold, rather than the substantially higher tensile strength of the material forming the bi-axially oriented container wall.
There is accordingly needed a carbonated beverage bottle or container with a pressure bottom and with an integral depending annular skirt which does not impair the strength of the vessel, as a pressure vessel, and which will support the container in a stable upright position.